Carl Heilman’s Photo Principles #2: Checking Exposure

Let’s dive right in! When checking exposure, the first two things to know are:

Making adjustments to the aperture diameter (f stop) and shutter speed affects the amount of light that reaches the sensor.

The ISO setting adjusts how sensitive the sensor is to the light falling on it.

Adjusting each of these settings in relation to the camera’s light meter reading is ultimately what affects the overall exposure of every photo.

There are two ways to check the exposure of a photo you have just taken. One is with the Highlights screen, and the other is with the Histogram.

Highlights:

The Highlights screen option, with its ‘blinkies’, is a real quick way to check for any overexposure issues in a photo. When viewing an image in Highlights during playback, any overexposed part of the image will flash from white to black. If this is only a very small section of a cloud, or a bright highlight point in the image, this flashing is OK. However, if large portions of the image are flashing, it’s time to adjust the exposure settings and take the photo again.

Depending on your camera, the Highlights screen may already be one of your Playback screen options. It may also have to be set up through Playback Menu options. Best to check your camera’s manual to find out for sure (note: the full manual may be available as a download if your camera only came with a synopsis).

Histogram:

The Histogram provides the most detailed information for the exposure of each photo. The far right edge of the histogram is the white point, and far left edge is black. If the graph line touches the white point, then some point in the image is white. That means, if there is a spike along the far right edge, there will be whole sections of the photo that are pure white, with no image detail.

So, if you have a photo where the brightest parts of the image are puffy clouds in the sky, and there is a spike along the far right edge of the Histogram, parts of those clouds will be pure white, with no cloud detail. This would be an overexposure issue. If shooting with an Auto-Metering mode, like aperture, shutter priority or program, then set the Exposure Compensation to a minus setting to compensate. If shooting in Manual, be sure to adjust any of the three setting options – aperture, shutter, or ISO – to reduce the light, and take the photo again.

Photo: A properly exposed image will have detail in the brightest part of the highlight areas. Note the spike along the right edge of the Histogram, showing considerable overexposure issues in this photo.

There is no ‘perfect’ curve to the graph itself; the graph line is simply a readout of cumulative tonal data throughout the photo. The line may have numerous peaks and valleys, and occasional spikes. The most critical points are at each end – the black point and white point, noting whether there are spikes at either end. Of these, the white point is most critical since it is not possible to pull lost highlight detail from an overexposed image during post processing (or in-camera processing if shooting jpeg). Thanks for reading!

More to come! “Checking Exposure” is the second entry in a 6-part series on landscape photo principles by renowned Adirondack photographer, Carl Heilman II. You can read the first entry here.

Over the next several weeks we’ll be diving deeper into even more. In the next entry, Carl will detail motion and depth of field. Down the line, we’ll also get tips on working with camera technology, photo composition and using a tripod, and how to be in the right place at the right time. Follow us on Facebook for updates on upcoming entries. Click here to read more about Carl Heilman II.